Okara is the pulp byproduct of soy milk production. The production, proximate composition, and uses of okara has been reviewed by O'Toole in “Characteristics and Use of Okara, the Soybean Residue from Soy Milk Production—A Review,” J. Agric. Food Chem. 1999, 47, 363-371, the disclosure of which is hereby incorporated by reference.
Briefly, in the traditional method of soy milk production, soy beans are allowed to swell by soaking in water. In the Japanese method, the hydrated beans are cooked and then ground to a colloidal paste, whereas in the Chinese method the hydrated beans are ground without cooking. In either case, the water soluble materials are extracted from the colloidal paste and used to make soy milk and tofu and the remaining insoluble material is filtered off. The insoluble residue is most commonly referred to as okara (Japanese), although it is also referred to as douzha (Chinese), bejee (Korean), tofukasu (Japanese), bean-curd refuse, or simply soy pulp.
It has been estimated that in Japan alone, nearly one million tons of okara are produced every year by the tofu industry. However, okara has found only limited use as a human food source due to its high water activity which facilitates rapid microbiological spoilage and renders it largely incompatible with most foods. Consequently, most okara is burned as waste, dumped in landfills, or used in animal feeds. This is unfortunate, not only due to the adverse environmental consequences, but because okara contains roughly 30% of the total solids, 20% of the protein, and 11% of the oil from the soy bean and thus represents a largely untapped source of nutrients, including soluble and insoluble fiber, protein, iron, calcium and other minerals, as well as beneficial isoflavones. In fact, the protein efficiency ratio of okara has been reported to be higher than that of other soy products, including soy milk.
Some attempts have been made to utilize okara as a direct food additive. For example, Waliszewski and co-workers investigated the effect of okara supplementation on the properties of corn tortilla by adding dried okara at levels of 5, 10, 15, 20, and 25% to nixtamalized corn flour. It was reported that enriched tortillas at levels higher than 10% of okara had unacceptable flavor. See Waliszewski, et al., J. Food Sci. 67 (8), 3194-3197 (2002).
The effect of dry okara on the specific loaf volume and hardness of bread made from wheat flour has also been investigated. See Rie Horiuchi, et. al, J. Integr. Stud. Diet. Habis, 16, 31 (2005). It was reported that the addition of 10% and 20% dry okara to wheat flour resulted in a decrease in loaf volume of 18.7% and 32.2%, respectively, and an increase in hardness from 0.24±0.04 Pa for the control (without okara) to 0.44±0.07 Pa and 0.9±0.05 Pa, respectively. Similarly, Bowles et al., “Physicochemical characterization of the soymilk by product—okara” Ciênc. Tecnol. Aliment., vol. 26, no. 3, p. 652-659 (July/September 2006) investigated the addition of dried okara to French type bread at 0, 5, 10, and 15% and report that sensorial analysis using a preference test favored the breads having lower levels of okara over the bread containing 15% okara.
Because of the high water-holding capacity and the off-taste often associated with okara, various attempts have been made to convert okara into forms more suitable for human food products.
Throughout Southeast Asia, okara has been fermented with the fungus Rhizopus oligosporus to make okara tempe, often called tempe gembus (Indonesian), which is eaten alone or added to other foods. Okara tempe has been reported to overcome some of the disadvantages of okara and is considered to have certain benefits including reduction in caloric intake, lowering of serum cholesterol levels, and high antioxidant activity. However, it has been reported that, while okara tempe is a good source of dietary fiber, the protein efficiency ratio of okara tempe is reduced as compared to okara. Furthermore, the range of food applications to which okara tempe can be adapted is limited.
JP 09-285,251 discloses a process for coating okara with shortening and the use of the resulting ingredient as a wheat substitute for cakes.
U.S. Pat. No. 5,690,981 to Anjinomoto Co. discloses a method for finely pulverizing okara to provide dietary fibers of rod-like shape of not greater than 5 microns in length. It is stated that the dietary fibers have reduced water-holding capacity due to their small size and can be used to reduce the caloric content of foodstuffs.
Several patents to Fuji Oil Company, including U.S. Pat. No. 5,587,197, U.S. Pat. No. 6,280,526, and U.S. Pat. No. 6,569,473 disclose a process for degrading okara under acid hydrolysis conditions to provide a water-soluble hemicellulose for inclusions in low-calorie food products.
Despite these advances, there is a continuing need in the art for modified okara compositions, particularly those having diminished water-holding capacity, for use as ingredients in foodstuffs.
It is therefore an object of the invention to provide methods for converting okara into forms more suitable for inclusion in food products. In particular, it is an object of the invention to provide modified okara compositions having diminished water-holding capacity as compared to unmodified okara, but which possesses many, if not all, of the nutritive benefits of okara.
It is further an object of the invention to provide food additives derived from okara which are suitable to augment the protein and/or fiber content of a variety of food products and which do not impart objectionable tastes or textures to conventional food products.